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One soil mistake could be preventing your seedlings from reaching their full potential.

If you're a gardener who likes to take the time to grow plants from seeds rather than buying established plants from garden centres, then at this time of year, you'll likely have small seedlings of your own which sprouted up in the seed trays on your windowsill or in a greenhouse.

But according to one gardening expert on social media, there's actually one thing that some gardeners get wrong when it comes to planting their seeds in trays. In fact, it's such a detrimental mistake that it could actually stop your plant from growing, meaning you'll never be able to enjoy the fully established result.

Toby Buckland shared a video on TikTok where he stressed the importance of getting your soil levels right when you fill up your pots. He said you may think you're saving money by skimping on soil, but not filling pots up to the brim could have dire consequences for your seedlings.

He said: "When sowing seeds, always fill your pots right up to the brim.

"I know loads of gardeners who save a few pennies by leaving the compost halfway up the sides of the pot. But you see, the rim of the pot shades the seedlings, and that means they stretch towards the light and they grow a bit like cress.

"They'll never recover from that. So, top them right the way up so it's level."

Toby also said you should give the pot "a good flood" with a watering can until the compost is soaked all the way through. He claimed you should know it's watered enough when it's "really heavy".

He added: "If you make sure it's completely saturated all the way through, you won't need to water that again until your seedlings are up."

Once your pot is fully watered, it's time to sow your seeds. Toby explained they should be sown "thinly" over the top of your soil, before sprinkling a small amount of soil on top to cover.

And the gardener also had a hack for evenly distributing your final sprinkle of soil. He recommended taking another pot and using the holes in the bottom of it as a "sieve" to gently shake soil onto the pot you're using.

Commenters on the post thanked Toby for his advice, although some said it unfortunately came too late, as their seedlings had already sprouted and were showing signs of stunted growth.

One person said: "Oh no! Great tip, but my seeds already sprouted, and are leggy." Another added: "Game changer! I've been gardening for nearly 50 years; every day's a school day." And a third wrote: "Fountain of knowledge!"

• Use a lightweight, well-draining seed-starting mix rather than garden soil, which can be compact and may harbour pests or diseases.
• Use seed trays, biodegradable pots, recycled containers (like yoghurt cartons), or any shallow container with drainage holes.
• For healthy, strong seedlings, give them 12-16 hours of light per day. Use grow lights or fluorescent lights if natural daylight isn't sufficient.
• Most seeds germinate best at temperatures between 18-24°C. Check seed packets for specific requirements and make sure you have good airflow, too.
• Keep the soil consistently moist but not soggy. Overwatering can lead to damping-off disease (a fungal issue that kills seedlings).
• Once the seedlings have two sets of true leaves, use a diluted liquid fertiliser (half-strength) every 1-2 weeks.
• Avoid overcrowding by thinning seedlings once they sprout their first set of leaves. Snip weaker seedlings at the soil line rather than pulling to avoid disturbing neighbouring roots.
• A week or two before moving your seedlings outdoors, gradually expose them to outdoor conditions. Start by placing them outside for a few hours a day in a sheltered spot, gradually increasing exposure to sunlight, wind, and cooler temperatures.